#include "segment/segment-graph.h"

bool operator<(const edge &a, const edge &b) {
	return a.w < b.w;
}

/*
* Segment a graph
*
* Returns a disjoint-set forest representing the segmentation.
*
* num_vertices: number of vertices in graph.
* num_edges: number of edges in graph
* edges: array of edges.
* c: constant for threshold function.
*/
universe *segment_graph(int num_vertices, int num_edges, edge *edges,
	float c) {
	// sort edges by weight
	std::sort(edges, edges + num_edges);

	// make a disjoint-set forest
	universe *u = new universe(num_vertices);

	// init thresholds
	float *threshold = new float[num_vertices];
	for (int i = 0; i < num_vertices; i++)
		threshold[i] = THRESHOLD(1, c);

	// for each edge, in non-decreasing weight order...
	for (int i = 0; i < num_edges; i++) {
		edge *pedge = &edges[i];

		// components conected by this edge
		int a = u->find(pedge->a);
		int b = u->find(pedge->b);
		if (a != b) {
			if ((pedge->w <= threshold[a]) &&
				(pedge->w <= threshold[b])) {
				u->join(a, b);
				a = u->find(a);
				threshold[a] = pedge->w + THRESHOLD(u->size(a), c);
			}
		}
	}

	// free up
	delete threshold;
	return u;
}